AJVR • Vol 80 • No. 8 • August 2019 727 I n veterinary medicine, the treatment of wild birds is challenging because of the scarcity of scientifc infor- mation with which to determine dosing regimens. Vet- erinarians involved in wildlife conservation sometimes use allometric scaling as a tool to make decisions on treatments for species in which few data are available. Frequently, allometric scaling is applied to estimate drug doses when pharmacokinetic data for the target species are not available. Special consideration must be given when a particular pharmacokinetic behavior is de- scribed for a specifc species (eg, obligate scavengers). This could be important because slow drug elimination in species of the Gyps genus has been reported. 1–3 Evaluation of allometric scaling as a tool for extrapolation of the enrofoxacin dose in American black vultures (Coragyps atratus) Samanta Waxman DVM, PhD Ana P. Prados DVM José J. De Lucas DVM, PhD Guillermo Wiemeyer DVM Laura Torres-Bianchini DVM Manuel I. San Andres DVM, PhD Casilda Rodríguez DVM, PhD Received November 17, 2018. Accepted January 29, 2019. From Facultad de Ciencias Veterinarias, Univer- sidad de Buenos Aires, Chorroarin 280, 1427 Buenos Aires, Argentina (Waxman, Prados); Consejo Nacional de Investigaciones Científcas y Técnicas (CONICET), Godoy Cruz 2290, 1425 Buenos Aires, Argentina; Departamento de Farma- cología y Toxicología, Facultad de Veterinaria, Uni- versidad Complutense de Madrid, Ciudad Univer- sitaria, s/n. 28040 Madrid, Spain (De Lucas, San Andres, Rodríguez); Ecoparque, R. de la India 3000, 1425 Buenos Aires, Argentina (Wiemeyer, Torres- Bianchini); The Peregrine Fund, 5668 W Flying Hawk Ln, Boise, ID 83709 (Wiemeyer); and Fundación Caburé-í, Sucre 2842, 1428 Buenos Aires, Argentina (Wiemeyer). Dr. Prados’s present address is Animal Clinic of Sierra de los Padres, Sierra de los Padres, 7601, Buenos Aires, Argentina. Dr. Torres-Bianchinni’s present address is Ministerio de Salud y Desarrollo So- cial, Av 9 de Julio, 1925 Buenos Aires, Argentina. Address correspondence to Dr. Rodríguez (rodfermc@vet.ucm.es). OBJECTIVE To determine the pharmacokinetics of enrofoxacin after IV administration in American black vultures (Coragyps atratus), to compare clearance of en- rofoxacin in American black vultures with clearance of this fuoroquino- lone in other avian species, and to evaluate whether allometric scaling is an appropriate tool for dose extrapolation in avian species. ANIMALS 6 healthy adult American black vultures. PROCEDURES Enrofoxacin concentrations were quantifed by use of high-performance liquid chromatography. Pharmacokinetics of enrofoxacin was determined in American black vultures after IV administration. Pharmacokinetic param- eters for 12 avian species obtained from 24 pharmacokinetic studies were used. Allometric analysis of enrofoxacin pharmacokinetic parameters was performed. RESULTS Volume of distribution at steady state for enrofoxacin was 3.47 L/kg, clear- ance was 0.147 L/h•kg, and elimination half-life was 18.3 hours. Compari- sons among avian species revealed that American black vultures had the lowest extraction ratio for enrofoxacin (1.04%). Only the volume of distri- bution at steady state and clearance had a good allometric ft. Goodness of ft was improved when ratites were not included in the analysis. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that the use of allometric scaling for the prediction of volume of distribution at steady state could provide a suitable method for extrapolation of enrofoxacin doses among avian species; however, allome- tric scaling could not be used to adequately predict the clearance of enro- foxacin. (Am J Vet Res 2019;80:727–735) The American black vulture (Coragyps atratus) is a New World vulture belonging to the order Cathar- tiforme. Its distribution includes the southern United States and South America, and it is classifed as least concern in the red list of threatened species. 4 Although this vulture species has genetic differences from mem- bers of the Gyps genus, the carrion-feeding lifestyle of vultures and the morphological convergence between Gyps spp and American black vultures, 5,6 which also can involve shared physiologic characteristics, could be refected in similar pharmacokinetic behavior of drugs. Enrofoxacin is one of the most widely used fuo- roquinolones in veterinary medicine. Because of its pharmacokinetic profle and spectrum of activity, enrofoxacin is an antimicrobial agent frequently ad- ministered to avian species in rehabilitation centers. It is commonly used to treat bacteremia or septice- mia and infections of the soft tissues, skin, bones and joints, urinary tract, respiratory tract, and reproduc- tive tract. 7,8 Although enrofoxacin has been exten- sively evaluated in avian species, no pharmacoki- netic studies have been performed with scavengers; ABBREVIATONS AUC Area under the plasma concentration–time curve Cl Clearance MBC Minimum bactericidal concentration MIC Minimum inhibitory concentration MPC Mutant prevention concentration MRT Mean residence time t 1/2β Elimination half-life Vd ss Volume of distribution at steady state Unauthenticated | Downloaded 02/24/23 02:28 PM UTC